Description: This native perennial plant is 3-7' tall and usually unbranched. The central stem is light green and glabrous, except where the whorls of leaves of occur, where it is slightly swollen and purple. There are 3-4 leaves in each whorl along the stem. The leaves are about 6" long and 3½" across, or sometimes larger; they are broadly lanceolate or ovate and serrated along the margins. Each leaf is dull green and hairless on the upper surface; the lower surface is hairless or finely pubescent. The foliage may be vanilla-scented, although this varies with the local ecotype.
The central stem terminates in one or
more panicles of compound flowers that are bunched together; this inflorescence
is usually more dome-shaped than flat-topped. Unlike the central stem, the
stalks of the inflorescence are sometimes finely pubescent. Each compound
flower consists of 5-8 disk florets and several overlapping series of bracts at
its base. There are no ray florets. The corolla of each disk floret is whitish
pink to purplish pink; it is tubular in shape and has 5 tiny teeth along its
upper rim. A divided white style is strongly exerted from each disk floret. The
floral bracts are pale pink and oblong. The blooming period occurs from
mid-summer to early fall and lasts about a month. Each floret is replaced by a
bullet-shaped achene with a small tuft of hair. These achenes are dispersed by
the wind. The root system is shallow and fibrous.
Cultivation: The preference is light shade to
partial sun, moist to mesic conditions, and a rich loamy soil. The leaves will
turn an unattractive yellowish green in the presence of strong
sunlight.
Range & Habitat: Sweet
Joe-Pye Weed occurs occasionally in most areas of Illinois, except for a few
counties in SE Illinois and elsewhere in the state, where it is uncommon or
absent (see
Distribution
Map).
Habitats include open woodlands, savannas, woodland borders, thickets,
partially shaded seeps, and partially shaded riverbanks. This plant can survive
in wooded areas that are somewhat degraded. However, populations have a
tendency to decline when the shade of overhead canopy trees becomes too
dense.
Faunal Associations: The
flower nectar attracts primarily long-tongued bees, butterflies, skippers, and
moths. Bee visitors include Bombus spp. (Bumblebees), Melissodes
spp. (Miner bees), and Megachile spp. (Large Leaf-Cutting bees).
Some bees also collect pollen. The caterpillars of various moths feed on
Eupatoriadelphus spp. (Joe-Pye Weeds), including Carmenta
bassiformis (Eupatorium Borer Moth), Emmelina monodactyla (Plume
Moth sp.), Perigea xanthoides (Red Groundling), and Schinia
trifasciata (Three-Lined Flower Moth). The Swamp Sparrow eats the seeds of
various Joe-Pye Weeds to a limited extent.
Photographic Location: A small opening in a wooded
area at Meadowbrook Park in Urbana, Illinois.
Comments: Sweet Joe-Pye Weed is one of the taller
wildflowers in wooded areas. It is often found in habitats that are more shady
and dry than other Eupatoriadelphus spp. (Joe-Pye Weeds) in the state.
To identify a Joe-Pye Weed, it is helpful to examine the central stem: the stem
of Sweet Joe-Pye Weed is solid in cross-section and purple where the leaf bases
occur, otherwise it is green and glabrous (see the lower photograph). The
species Eupatoriadelphus maculatus (Spotted Joe-Pye Weed) has solid
stems that are purple-spotted or solid purple throughout and occasionally
hairy, while Eupatoriadelphus fistulosus (Hollow-Stemmed Joe-Pye Weed)
has hollow stems that are glabrous and glaucous. Sweet Joe-Pye Weed usually has
only 3-4 leaves per whorl, while Spotted Joe-Pye Weed has 4-5 leaves per whorl
and Hollow-Stemmed Joe-Pye Weed has 4-7 leaves per whorl. The Joe-Pye Weeds
have been assigned to their own genus; in the past, they were assigned to the
Eupatorium genus of the white-flowered Bonesets.